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The typography of source code

Take a look at the following source code, can you guess which language this is written in?

It’s CSS. CSS has a typical layout with a minimal indentation depth where a group of selectors embraces lines of attribute / value pairs. Take a look:

As with the example above all of our source code has typical (macro) typographical properties. This features can tell us something about the language used, about the type of artifact and even about the composition of the individual parts of a class or file itself.
Here’s another typical file in a common language:

In this case it is a Java class. It reveals itself by its block of imports at the top (1). The class declaration (2) is rather long probably due to generics. The typical block of field declarations (3) starts the class body. Quickly a short constructor follows (4). It is too short but has parameters so it is a convenience constructor. The real constructor is next (5). Here we see the constructor is too long. It does so much we almost take it for a normal method. At (6) we see parameters for a method call one on each line. The slight change in indentation at (7) indicates an inner class. The block at (8) confirms the inner class: here parameters from the outer class are referenced by prefixing it with OuterClassName.this.
Even subtle things like annotations (9) can be seen at macro level.

Let’s compare two object oriented languages one is Java, the other one Ruby.

Several things can be noticed (besides the Java version is much longer than the Ruby one). First the Java block of imports is missing in Ruby. The field block seems to be small in Ruby but another big block follows in the middle. The Ruby class shown here is a Rails domain class. The block in the middle contains the associations (has_many and friends). Looking closer one can glimpse that the closing part of the methods seems a bit thicker in Ruby (Ruby closes the method with end whereas Java closes with }). But besides the difference a similarity is also there: both classes have a couple of short methods near the bottom.
Even within one language and one framework classes with different purpose have different shapes. Seeing a Rails model and a controller side by side shows some interesting patterns.

While controllers have a block at the end of the class (which is for permitting request parameters), model classes have blocks of scope declarations and associations typical at the center. Whereas model methods are short in both dimensions, the controller methods have a level of indentation (which is a typical if which checks for the success or failure of the operation).

But why does this all matter? The first thing when we look a block of text is its (macro) structure. Typical patterns can help us to identify the type of class or language. Inconsistencies could be bugs or parts which were difficult to write. Kevlin Henney advocates in his talk Seven Ineffective Coding Habits Of Many Programmers for formatting techniques that are stable and produce a minimal set of alignments. Because:

You convey information by the way you arrange a design’s elements in relation to each other. This information is understood immediately, if not consciously, by the people viewing your designs.